It is known that a convenient means for quickly gathering information relative to an extensive area of the terrestrial globe consists in providing on a satellite moving relative to the earth a receiver apparatus adapted to receive radio information coming from a plurality of beacons distributed over the zone overflown by the satellite.
An object of the invention is to provide a method for gathering and processing large amounts of radio information while calling upon a simple apparatus for equipping both the beacons and the satellite.
The beacon transmitters which may have identical or very close nominal frequencies from which the real frequencies deviate by reason of the different ageing of the transmitters or variations of climatic conditions, transmit messages at regular or irregular time intervals, the messages customarily being of unequal durations.
In any event the messages transmitted by the beacons reach the satellite at unanticipated moments, or asynchroneously, and an object of the invention is to take best advantage of the equipment of the satellite in order that the gathering of data contained in the messages is effected at maximum speed and efficiency while preserving equipment of great simplicity.
According to an object of the invention, the equipment of a satellite comprises a plurality of radio processing devices each of which is adapted to extract the information from a received message and it is characterized by the fact that the equipment comprises a management unit which adapts the processing devices to the determined frequency of a message in the course of reception and directs said message to that one of the processing devices which is best able to effect the processing.
It provides a receiving and management unit which determines for each message received its frequency value and its level value, which gives preference to messages at high level over those at lower levels, which directs a message of a frequency value to a processing device previously adapted to said value and which after the beginning of processing by said device, inhibits the routing of other messages to said device.
The invention is of particular interest in case the information translated by phase modulation of a carrier wave and it provides carrying out at the receiving and management apparatus, upstream of the processing devices, a sufficiently accurate estimate of the frequency to direct a message to a processing device having a phase locked loop (PLL) which is operational with respect to the frequency of said message and it then provides allocating said message definitively to said processing device only after the phase locked loop of the device is set at the carrier frequency with the accuracy required for handling the characteristic phase modulation of said message.
According to the invention, also, there is provided before definitive allocation to a processing device, routing to said device any signal whose frequency is in the operational band of its phase locked loop and whose level is greater than that of a signal already assigned said device.
By this "conditioned freedom" of the link between the receiving-management apparatus and the processing device, the processing device is automatically brought into precise frequency accord required for the demodulation, and simultaneously, optimum efficiency is conferred on the equipment while assuring the reading of the messages which are the best received and thus do not risk being disturbed, the occupation of said device thus having a surely useful result.
Satellite equipment according to the invention not only permits the gathering of information from the different messages received but also the locating of the beacons transmitting said messages, while taking advantage of the Doppler effect, which affects all messages received and without which it would be necessary to provide particular arrangements for this purpose.